Line pole grounding system

ABSTRACT

An improved grounding system for line pole crossarms is provided to reduce line pole fires due to leakage currents. A pair of crossarm bands having an adhesive conductive material on their inner surface are wrapped around the crossarms spaced on opposite sides of the pole, and grounding means shunts the leakage currents to ground around the gains where the arm meets the pole.

United States Patent 2,331,098 10/1943 Whiteetal.

Inventor William H. Duvendack Butte, Mont. App1.No. 51,221

Filed June 30, 1970 Patented Nov. 16, 197l Assignee Joslyn Mfg. andSupply Co.

Chicago, Ill.

LINE POLE GROUNDING SYSTEM 5 Claims, 8 Drawing Figs.

US. Cl 174/6, 174/40 CC, 174/45 R, 339/251, 339/278 C Int. Cl HOZg 7/00,H0 1 r 3/06 Field of Search l74/2, 6,40 R, 40 CC, 45 R, 117 A; 339/251,278 R, 278 C References Cited UNITED STATES PATENTS 2,399,899 5/1946Tinnerman 174/40 CC 2,427,883 9/1947 Score et a1. 1 174/40 CC 2,808,35210/1957 Coleman et a1... 174/117AUX 2,844,643 7/1958 Cofer et a1 174/63,344,225 9/1967 Jureit et a1. 174/45 R OTHER REFERENCES ElectricalWorld, Straps and Washer Stop Pole-Top Fires," Vol. 141, No. 22, pages92 and 98. TKIE6. Copy in 174' 45R,

Primary Examiner-Laramie E. Askin Attorney-Mason, Kolehmainen, Rathburn& Wyss ABSTRACT: An improved grounding system for line pole cross-armsis provided to reduce line pole fires due to leakage currents. A pair ofcrossarm bands having an adhesive conductive material on their innersurface are wrapped around the crossarms spaced on opposite sides of thepole, and grounding means shunts the leakage currents to ground aroundthe gains where the arm meets the pole.

LINE POLE GROUNDING SYSTEM The present invention relates to an improvedline pole apparatus, and more particularly, to means designed to directleakage current from the arms of a line pole to ground.

Heretofore, difficulty has been experienced with pole fires due toleakage currents. Pole fires have been an increasing problem and areparticularly intolerable since the line may travel through remote,almost inaccessible areas where repair is extremely difiicult, costlyand time consuming. In a typical bumdown, the juncture of the arm and apole catches fire until the arm breaks away from the pole, after whichthe fire generally goes out. Examination shows that the arm and pole areboth badly charred in the gain area around the through bolt. The side ofthe arm facing the pole generally has a cratershaped burn centeringaround the bolt hole, while the pole generally has a large pocket-burnin the same area and the bolt hole is charred and enlarged. The armbreaks away from the pole either because it weakens and cannot supportthe load, or because the bolt becomes so hot that it softens and fails.

Most fires seem to occur after long, dry spells when dust contaminationhas an opportunity to build up on the surfaces of insulators andcrossarms. Then, when moisture from alight rain or condensation wetsthis dust, surface resistivity is reduced by hundreds or thousands oftimes and high leakage occurs. The fact that high leakage occurs is notnecessarily harmful as long as the entire leakage path is wetted.However, if portions of the pole and crossarm, especially near thejuncture of the two, are shaded from moisture and remain relatively dry,line voltage or very near line voltage may be impressed across a highresistance area only inches wide. High IR losses at this point initiatearcing and subsequent burning. Currents of only 8 milliamps aresufficient under the right conditions to cause ignition.

But even arcing and tracking in a dry area will seldom result in a fireif they occur on the outside surfaces of the arm or pole where the heateither may be radiated out or convected away by the wind. On the otherhand, if the arcing takes place in the gain area where heat can beconfined and radiated from one surface to another, serious burning islikely to occur.

Heretofore, several methods have been proposed for eliminating polefires. An effective method would be to ground the suspension insulators.This is particularly impractical on existing lines because additionalinsulator bells would be required, reducing ground clearance andincreasing the radius of line swing. Moreover, such additionalinsulators on new lines are costly and require redesign of the linesstructure.

It has also been suggested to install a high-impedance plastic gainbetween the pole and arm to force arcing to occur over the outside ofthe arm to the grounded through-bolt where it can be easily removed.However, this method is also impractical in existing installationsbecause the installation of the gain would have to be done with the linedeenergized, and the cost of assembling and reassembling all of thestructures on an existing line would be prohibitive. Moreover, theinstallation of a high-impedance plastic gain on new line constructionis both costly and would require redesign of the pole line apparatus.

Accordingly, it is an object of the present invention to provide a newand improved line pole apparatus for directing crossarm leakage toground.

Yet another object of the present invention is to provide a line poleapparatus which shunts leakage currents from the crossarms to groundaround the gains.

Yet another object of the present invention is the provision of a newand improved line pole apparatus minimizing pole fires due to leakagecurrents from the crossarms.

Still another object of the present invention is the provision of a newand improved line system for directing leakage currents from thecrossarms around the gains of the pole.

Further objects and advantages of the present invention would becomeapparent as the following description proceeds and the features ofnovelty which characterizes the invention will be pointed out withparticularity in the claims which form a part of this specification.

In accordance with these and other objects, there is provided animproved line pole apparatus directing leakage currents from a crossarmof a line pole to ground around the gains of the pole. Morespecifically, there is provided a pair of armbands, spaced on oppositesides of the pole, with resilient conductive material on the innersurface of the bands providing a substantially continuous electricalpath between the band and the arm. The arms in turn are grounded aroundthe gains of the pole. In a preferred embodiment of the invention, theconductive material is bonded to the band in a scalloped-shaped moldingso that the molding on the band with the band in place on the cross armis thickest at the center of the flats of the crossarm and thinnest atthe corners thereof.

Advantageously, the armband according to the present invention insurescontact with the wood throughout the length of the band as the dimensionof the arm changes due to moisture content and the temperature and age.

For a better understanding of the present invention, reference may behad to the accompanying drawing wherein:

FIG. 1 illustrates a line pole apparatus including a utility pole andcrossarm joined by a through bolt, and incorporating the presentinvention;

FIG. 2. is a cross-sectional view of the line pole apparatus taken alongline 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view taken FIG. 2;

FIG. 4 illustrates a preassembly of bands and grounding straps accordingto the present invention;

FIG .5 is a side elevation view of the armbands shown in FIG. 4;

FIG. 6 is a cross-sectional view of the armband line 6-6 in FIG. 5; and

FIG. 7 is a cross-sectional view of the armband taken along line 7-7 inFIG. 5; and

FIG. 8 is a cross-sectional view of the armband shown in FIG. 5 havingan uncured conductive sealant.

Referring now to the drawings, and particularly to FIG. 1 thereof, thereis illustrated a line pole apparatus 10 incorporating the presentinvention. The line pole apparatus 10 includes a utility or line pole l1and a crossarm 12 connected thereto by a through bolt 13. A known typeof wire clamp 14 is secured to the arm end of the through bolt 13. Agrounding wire I5 runs from the top of the pole to a suitable ground.

In accordance with the present invention there is provided an improvedarm band assembly 20 for directing leakage currents from the crossarm 12to the ground over the gain area of the line pole apparatus 10.Referring more specifically to FIG. 4, the armband assembly 20 includesa pair of spaced armbands 21 and 22 having a suitable banding buckle 23at one end and interconnected by a cross conductor 24. The crossconductor 24 may be spot welded to the armbands. A grounding strap 25 isjoined to the cross conductor 24 in any suitable manner such as bywelding, as illustrated in FIG. 4. The armbands 21 and 22, buckle 23,cross conductor 24, and grounding strap 25 may, of course, be of anysuitable conducting material, and stainless steel has been found to workadvantageously. To insure contact between the armbands 21 and 22 and thewood arms through the length of the bands, the armbands contain suitableconducting resilient material 28 on its inner surface formed in ascalloped shape so that when the band is in place, the conductingmaterial 28 is thickest at the center of the flat faces 12a, 12b, 12c,and 12d of the crossarm, and thinnest at the comers.

In a particular embodiment of a strap configuration, as best illustratedin FIG. 5, for a crossarm having approximately 9.4 by 5.4 inch crosssection, it has been found that formation of a conducting resilientmaterial 28 to a minimum thickness t of 0.175 inch and a maximumthickness t at the high point of 0.625 inch performs satisfactorily.Under such a geometric configuration, the radius of curvature along thelong arms r, is about 25 inches, and the radius of curvature of theconducting resilient material along the short walls is about 7 /2inches.It has been found that a silicone rubber adhesive-sealant, such as alongline 3-3 of taken along Dow Corning Corporation No. 735, formssatisfactorily for the conductive resilient material 28.

The band may be fabricated with the conducting resilient material byfirst laying a length of stainless steel flat in a bottom of a woodenmold, the top of which is cut in a scalloped configuration. Next, asuitable quality of conductive resilient material 28 such as siliconerubber adhesive-sealant is squirted into the mold with a suitablecaulking gun, and a tool is run over the top of the mold to conform theconducting resilient material 28 into a scalloped-shaped form having agroove 29. The adhesive-sealant is then cured. and because the rubber isnonslumping, the assembly may be immediately removed from the mold andeither hung up or laid down to cure at room temperature.

The conductive silicone rubber sealant is easy to work with, hasadequate conductivity, has good weather and sunlight resistance, andwithstands the high temperatures to which it may be exposed duringarcing. The material also bonds well to stainless steel, even without aprimer.

Installing the banding system on a crossarm is a relatively fast andsimple operation which can be done with the line energized. Referring toFIG. 2, the lineman preferably first wraps around the arm, and staplesdown, a strip of common copper screening 30 at a point of about inchesfrom the center of the pole. Several inches overlap is allowed so that aground conductor can be sandwiched in between. Next, the lineman placesan uncured adhesive sealant 280, which can be of the same type as thematerial 28, into the groove 29. Finally, the band is placed in placeover the screening around the arm and tightened and locked with abanding tool.

The use of screening is advantageous for a number of reasons. It tendsto pick up the leakage current first and therefore keeps arcs away fromthe conducting resilient rubber. lt conducts away heat that may begenerated in the rubber. It makes a lower resistance contact with theground than is possible with a conductive rubber alone. The uncuredconductive sealant 28a is preferably placed into the groove 29 to insureintimate contact between the band, the screening and the wood.

After the bands 21 and 22 have been secured to the crossarm, thegrounding strap 25 may be grounded to the through bolt 13 by means ofthe were clamp 14, as best illustrated in FIG. 1, and may be grounded tothe pole ground 15 by a suitable connector clamp 32.

It has been found that pole fires due to leakage currents aresubstantially eliminated by the application of the arm band assemblyaccording to the present invention.

Although the present invention has been described by reference to only asingle embodiment thereof, it will be apparent that numerous othermodifications and embodiments may be devised by those skilled in theart, and it is intended by the appended claims to cover allmodifications and embodiments which fall within the true spirit andscope of the present invention.

What is claimed as new and desired to ters Patent of the United Statesis:

1. An arm-grounding system for a line pole crossarm wherein a crossarmis joined (thereto) to a line pole by a through bolt, said systemcomprising:

a pair of armbands for a pole arm adapted to be spaced on opposite sidesof a pole,

a resilient conductive material on the inner surface of said bands forproviding a substantially continuous electrical path between the bandand an arm throughout the length of each band, and

means for grounding said bands.

2. The system defined in claim 1 wherein said conductive material isconductive silicone rubber sealant.

3. The system defined in claim 1 wherein said conductive material is anadhesive.

4. The system defined in claim 1 in combination with utility pole, acrossarm, and a through bolt securing said crossarm to said pole, saidbands being wrapped around said arm on opposite sides of said pole.

5. The system defined in claim 1 wherein said conductive material isbonded in a scalloped-shaped molding to said bands so that when the bandis in lace on a crossarm, the material is thickest at the center of theflats of a crossarm and thinnest at the corners to provide compressiveforce distributed all around the arm.

be secured 20 by Let-

1. An arm-grounding system for a line pole crossarm wherein a crossarmis joined (thereto) to a line pole by a through bolt, said systemcomprising: a pair of armbands for a pole arm adapted to be spaced onopposite sides of a pole, a resilient conductive material on the innersurface of said bands for providing a substantially continuouselectrical path between the band and an arm throughout the length ofeach band, and means for grounding said bands.
 2. The system defined inclaim 1 wherein said conductive material is conductive silicone rubbersealant.
 3. The system defined in claim 1 wherein said conductivematerial is an adhesive.
 4. The system defined in claim 1 in combinationwith utility pole, a crossarm, and a through bolt securing said crossarmto said pole, said bands being wrapped around said arm on opposite sidesof said pole.
 5. The system defined in claim 1 wherein said conductivematerial is bonded in a scalloped-shaped molding to said bands so thatwhen the band is in place on a crossarm, the material is thickest at thecenter of the flats of a crossarm and thinnest at the corners to providecompressive force distributed all around the arm.